Evolutionary and dual inheritance models of initiation and use of psychoactive substances, including novel psychoactive substances

Introduction: Research into drug use has typically been restricted to studies of proximate models (i.e. biological mechanisms). However, an evolutionary/ultimate perspective may be uniquely relevant to understanding drug-seeking behaviours.
In fact, a range of competing evolutionary models have emerged which explain why humans evolved through natural selection to use psychoactive substances.
Objectives: We aimed here to critically review evolutionary, cultural and dual inheritance perspectives on drug initiation and use, including considerations on novel psychoactive substances (NPS).
Methods: A literature search was conducted usingusing key resources including PubMed with a focus on drug use and human population data. This was supplemented by personal archives.
Results: A range of evolutionary models of why humans initiate and continue using psychotropic substances was identified. They include: a) Increasing reproductive fitness; b) Psychotropic self-medication (pharmacological manipulation of emotions); c) Pharmacophagy and infection control; d) Mismatch theory; e) Evolutionary Constraints; f) Trade-offs; g) Costly Signalling and Handicap theories; h) Placebo, ritual and healing effects; i) Drug use in spirituality or religion (e.g. the role of psychedelic drug use by “neoshamans”
and “psychonauts”). Some of these models are conceptually similar or overlapping.
They are not mutually exclusive and may interact in unpredictable (i.e. non-linear) ways.
Conclusions/Importance: Evolutionary, cultural and dual inheritance models of drug initiation and use reveal functional origins and adaptive advantages of psychotropic drug use. An evolutionary perspective is particularly helpful in understanding the specific dangers of the new phenomenon of NPS. Evolutionary perspectives suggest new directions for research and treatment.